I've been having a hip-hop midlife crisis of late, and my grado sr-125's have been great for my habit.
That said, I was just slumming around GoodGuys(yesterday) and came away with a pair of open-box HD580's.
The bass is quite different: to start, tight and fast. But not as enveloping.
The vocals are, as have been said before, transparent; and up-front. I have found this to be very different from my Grado's, where all tracks seem to have equal weighting, and dispersed (a sound i love, btw). I can absolutely follow the phrasing and interpreting of the doseone, cannibal ox, el-p, etc; along with the beats, which is something that I COULD NOT DO with my Grados.
If you are listening to more underground stuff (defjux, anticon), i think this articulation of the vocals is a benefit. People speak of the anemicness(sp?) of the bass on the 580/600s. My suspicions point toward a lack of amp on this point.
However, I can't listen to any of it on the HD580's without a crossfeed somewhere in the source chain. This I can't explain.
All that said, for the low(?) prices of a pair of 580's at many places, it might give you a different slant on what you are listening too / for whatever reasons you might be doing it.
They are still an open phone, which is a bonus for me.